An aromatic polycarbonate sunglass lens is typically produced by punching a functional sheet, in which an aromatic polycarbonate sheet or film is used as a protective layer of a functional layer such as a polarizing film layer or a photochromic layer, into a desired shape, heat-bending the punched piece into a partial sphere, injection-molding an aromatic polycarbonate for lenses onto a concave surface side of the partial sphere, and performing a surface treatment or the like as needed.
A protective film is attached to this functional sheet so that the surface of the functional sheet is protected from contamination and foreign matter during distribution, processing steps, etc. In particular, there has been proposed a polyolefin protective film that can withstand heat-bending in a high-temperature environment near the glass transition temperature of the aromatic polycarbonate (PTL 1 and PTL 2).
PTL 1 discloses a double (structure) protective film in which a polyolefin film having a substantive melting point of 150° C. or higher is provided as the surface layer and a polyolefin film having a substantive melting point of 125° C. to 145° C. is provided as the film layer for adhesion or bonding.
PTL 2 discloses a co-extruded polyolefin film as a protective film, in which the polyolefin film has a melting peak (A) at 105° C. to 130° C. and a melting peak (B) at 160° C. to 175° C. and the melting peak area ratio [(A)/(B)] is 35/65 to 80/20.
PTL 1 and PTL 2 describe evaluation (effects) after heat bending but do not mention the injection-molded lens prepared by loading a heat-bent product to an injection molding mold or evaluation of the injection-molded lens.
When such a protective film-attached functional sheet is punched into a desired shape and heat-bent to form a partial sphere or the like, the heat-bent product is loaded on an injection molding mold, and an aromatic polycarbonate for lenses is injection-molded onto a concave surface from the gate at the side surface to prepare a lens molded product (hereinafter referred to as an injection lens), streaks of white color (hereinafter referred to as white streaks) sometimes occur and this has been recognized as an appearance defect, which poses a problem.
In particular, as demand for improving productivity increases, the requirements posed on the production, such as improved operation efficiency of equipment and a shorter production time, have become increasingly severe. As such issues are addressed, the frequency of occurrence of “white streaks” defects has shown an increasing tendency and an urgent solution is desirable.